1. Field of the Invention
This invention lies in the field of liquid treatment systems. More particularly, it concerns the treatment of waste water with air, in order to improve the biological oxygen demand. Still more particularly it comprises an apparatus for efficiently aerating a liquid such as water to supply the biological oxygen demand.
2. Description of the Prior Art
It is common today to find liquids which are produced in quantity to be unsuited for discharge to commonly found waterways because of the biological oxygen demand for the organic material contained in the liquids. These effluent streams may be products of sewage treatment, typically, or they may result from certain chemical processes. It is vitally necessary for these effluent streams to be processed for reduction in biological oxygen demand before they can be vented to waterways in order to avoid very serious pollution of the waterways. It is common, today, to find reduction of biological oxygen demand (BOD) through aeration of the liquid effluents where air is caused to bubble upwardly through the liquids so that the oxygen content of the air can supply the BOD for the liquid so that the BOD can be satisfactorily supplied before the liquid, which is aqueous in nature, is released to a commonly-found waterway as a required disposal means.
Because the air is bubbled upwardly through the liquid, the oxygen of the air becomes available to the liquid at the surface of each bubble. Because the air is forced into the liquid at some depth within the liquid, the bubbles as formed are subjected to the pressure (statichead) of the liquid head and are small as formed at full liquid depth. But as buoyancy forces the bubble to rise, the size of the bubbles increases with rise. Therefore, the greater the number of bubbles formed as air enters the liquid, the better the air-liquid contact, which result in greater oxygen delivery to the liquid within a fixed time period, which can be defined as the time period during which liquid is exposed to air within the aeration vessel, or the time interval from liquid entry to the vessel to exit from the vessel.
Numerous devices have been constructed in the prior art for contacting a liquid with air, such as bubbling air up through a tank water or creating a spray of liquid into the air, and so on. All of these have limitations such as the residence time required to get the required amount of oxygen into the liquid, or the expense of energy for the processing of the liquid, and so on.